Accumulators are well known apparatus used in a variety of engineering fields as a means by which energy can be stored and are sometimes used to convert a small continuous power source into a short surge of energy or vice versa. Accumulators may be electrical, fluidic or mechanical and may take the form of a rechargeable battery or a hydraulic accumulator, capacitor, compulsator, steam accumulator, wave energy machine, pumped-storage hydroelectric plant or the like.
Hydraulic accumulators are produced in numerous forms including piston accumulators, bladder accumulators, diaphragm accumulators, weighted and spring-loaded accumulators. One of the primary tasks of hydraulic accumulators is to hold specific volumes of pressurized fluids of a hydraulic system and to return them to the system on demand. However, hydraulic accumulators may also be configured to perform a plurality of tasks including, energy storage, impact, vibration and pulsation damping, energy recovery, volumetric flow compensation, and the like.
There are inherent restrictions in any hydraulic system powered by a pump configured to provide a predetermined continuous power. While a more powerful pump will have the capacity to pump hydraulic fluid faster at a given pressure, it also requires more energy. A hydraulic accumulator normally allows the system to accommodate a rapid surge in internal pressure via its storage of pressurized hydraulic fluid, avoiding damage to the system.
Typical hydraulic accumulators are storage chambers into which hydraulic fluid is pumped by a hydraulic pump, often to relieve excess pressure elsewhere in the hydraulic circuit. The accumulator may include a further valve through which the stored fluid outputs into the rest of the hydraulic system. In gas accumulators, a pressurized gas bladder presses against a hydraulic bladder. As the hydraulic bladder fills, it compresses the gas in the gas bladder, thus increasing the stored pressure. A spring accumulator operates in a similar manner, with the exception of a large spring or springs applying the compressive force against the hydraulic bladder. In a raised weight accumulator, the hydraulic fluid is pumped into a weighted piston. Thus gravity exerts a constant force on the fluid, compressing it as it fills the piston and assisting emptying of the piston.
Typical prior art gas accumulators consist of a fluid chamber connected to a hydraulic system and a pre-charged gas chamber. The chambers are separated by a bladder, piston, or any kind of elastic diaphragm.
If the fluid pressure at the inlet to the accumulator fluid chamber becomes higher than the pre-charge pressure, fluid enters the accumulator fluid chamber and compresses the gas, thus storing energy. A drop in the fluid pressure at the inlet forces the stored fluid back into the system.
If pressure at the accumulator fluid chamber inlet drops below the gas chamber pressure, the gas chamber becomes isolated from the system by the inlet valve. In such situations, pressure in the gas chamber remains constant and equal to the pre-charge pressure value, while pressure at the inlet depends on pressure in the system to which the accumulator is connected.
Similarly, for a typical prior art spring-loaded accumulator, fluid entering the accumulator fluid chamber compresses the spring, thus storing energy. Since the compressive force of the spring increases as fluid enters the chamber and decreases as the accumulator is discharged, the resultant pressure is not constant. As the spring is preloaded, fluid only starts entering the chamber after the inlet pressure exceeds this threshold.
United States patent publication number US 2010/0018196 A1 is an example of an existing accumulator.
Thus, it can be seen that prior art accumulators are primarily directed at improving consistency of power output by taking some of the peak power of a cyclic operation and re-introducing it into portions of the cycle with a lower-power availability. However, this does not assist in cyclic operations with the converse requirements, i.e. cyclic operations with non-constant power requirements. In particular, prior art accumulators do not assist cyclic operations where there is unutilised available power during portions of the cycle, whilst additional power is highly desirable at other portions of the cycle.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein; this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.